The present invention relates generally to the field of medical devices for handling radioisotope materials. More specifically, the present invention relates to an automated radioisotope seed cartridge for transporting and handling low dose radioisotope seeds for use in brachytherapy procedures or the like.
The use of radioisotopes for various medical procedures such as brachytherapy and the like is well known. Such uses fall into two general categories: (i) high dose radioisotopes which are temporarily positioned in relation to a patient""s body for a relatively short period of time to effect the radiation treatment, and (ii) low dose radioisotopes which are permanently implanted in a patient""s body with the duration of the radiation treatment determined by the strength and half-life of the radioisotope being implanted. High dose radioisotopes are typically implanted using a catheter arrangement and a device commonly known as an afterloader that advances the high dose radioisotope located on the end of a source wire through the catheter to the desired location. Low dose radioisotopes, on the other hand, are implanted using an array of implant needles with the low dose radioisotopes being encapsulated in very small containers known as seeds that are manually loaded into a series of implant needles and then ejected to form a three-dimensional grid of radioisotopes in the patient that corresponds to a dose plan as determined by the physician. The goal of the low dose brachytherapy procedure is to position this three-dimensional grid of radioisotopes seeds in and around a target cancerous tissue area. Each of the radioisotope seeds consists of a radioactive source such as Iodine (I-125) or Palladium (Pd-103) inside a small tube-like titanium shell that is about the size of a grain of rice. These type of low dose radioactive sources emit a very low energy radiation that is primarily absorbed by the tissue immediately surrounding the radioisotope seed. This constant low energy radiation is typically emitted by the radioisotope seeds for a period of up to six months as a way to kill the cancer cells in the target area without having to subject the patient to the discomfort and risks that often accompany high dose radioisotope procedures.
One common brachytherapy procedure is the use of low dose radioisotopes to treat prostate cancer. Although brachytherapy procedures using low dose radioisotopes can be applied to many different parts of the body, it is helpful to describe a particular treatment to gain a better understanding of these treatments. In a typical prostate cancer procedure, a predetermined number of seeds (between 1-6) are positioned within each of a series of implant needles (up to 40), with the seeds being spaced apart in each needle by small spacers. A small amount of bone wax is positioned on the tip of the implant needles to prevent the seeds and spacers from falling out until they are implanted in the patient. The loaded implant needles are then positioned at the appropriate location for insertion into the perineal area of the patient using a stand that has an X-Y coordinate grid. Each needle is manually positioned in the appropriate chamber in the grid and is inserted into the patient. An ultrasound probe is used to assist the physician in guiding each of the needles to the desired location. The seeds and spacers are delivered from the tip of the implant needle using a stylet and hollow needle arrangement where the hollow needle is preferably retracted while the stylet remains in place. When completed, the implanted seeds form a three-dimensional grid of radioisotope sources that implements a predetermined dose plan for treating the prostate cancer in the patient. For a more detailed background of the procedures and equipment used in this type of prostate cancer treatment, reference is made to U.S. Pat. No. 4,167,179.
Over the years there have been numerous advancements in the design of equipment for use in radioisotope procedures. U.S. Pat. Nos. 4,150,298, 5,147,282, 5,851,172 and 6,048,300 describe replaceable cartridge assemblies that contain the source wire used in conjunction with specifically adapted afterloaders that advance the source wire into a catheter systems for high dose radioisotope procedures. U.S. Pat. No. 4,759,345 describes a shielded loading assemblies for hand implanted hypodermic needles. U.S. Pat. Nos. 4,815,449 and 4,763,642 describe a seed carrier that prepositions and encases a series of seeds in a body absorbable material. U.S. Pat. No. 5,906,574 describes a vacuum-assisted apparatus for manually handling and loading radioisotope seeds within a visible radiation shield. The same company which provides the vacuum-assisted apparatus described in U.S. Pat. No. 5,906,574, also provides an Indigo(trademark) express seeding cartridge that is a tube with seeds prepositioned in the tube such that the tube accurately indexes and positions individual seeds in the well chamber of a radiation detector for purposes of calibrating the radioisotope seeds.
U.S. Pat. Nos. 4,086,914, 5,242,373 and 5,860,909, as well as PCT Publ. No. WO 97/22379, describe manual seed injector arrangements for a low dose radioisotope procedure that utilize drop-in seed cartridges or seed magazines to supply the seeds directly to an implant needle arrangement that is specifically adapted to such cartridges or magazines. U.S. Pat. Nos. 4,086,914, 5,242,373 and PCT Publ. No. WO 97/22379 describe seed cartridges in which the radioisotope seeds are maintained in an end-to-end relation to each other within the cartridge. The cartridge is positioned in an aligned, colinear relation with the bore of a needle and a manual push rod arrangement is used to eject the seeds from the cartridge. In U.S. Pat. No. 5,860,909, the cartridge is mounted above a magazine arrangement of an implant needle where the radioisotope seeds are maintained in a stacked side-by-side relation to each other within the cartridge. As a new seed is to be implanted, the bottom seed of the stack is released into the magazine and then ejected from the needle.
Although such replaceable cartridges have been well received for use in connection with high dose radioisotope procedures, the standard techniques for low dose radioisotope procedures continue to utilize a series of preloaded implant needles that are manually loaded by a radiophysicist at the hospital just prior to the procedure. There are several reasons for why manual loading of the implant needles just prior to use in low dose radioisotope procedures is preferred. First, there are differences in the types of radioisotope sources that do not favor use of a cartridge arrangement for low dose radioisotope procedures. The source wires used for high dose radioisotope procedures use only one or a small number of very high power radioisotope sources having relatively long half-lives. As a result, it is cost effective and practical to provide for a cartridge arrangement for such a small number of high dose radioisotopes that can be preordered and maintained at the hospital well in advance of a procedure. In contrast, given the relatively short half-lives of the radioisotopes used in low dose radioisotope procedures it is preferable that the radioisotope seeds be sent to the hospitals by overnight delivery for use the next day. Because the number of radioisotope seeds varies from procedure to procedure depending upon the dose plan and because the cost of each low dose radioisotope seed is significant, it is not cost effective to order more radioisotope seeds than will be used in a given procedure. Second, it is important to minimize the time of the procedure, both in terms of the exposure time of the physician to the low dose radioisotope seeds and in terms of the total time of the procedure from the economics of medical practice. The existing drop-in cartridge and seed magazine systems described above take longer to perform the implant procedure than using conventional preloaded implant needles because the radioisotope seeds are implanted one-by-one, rather than being delivered simultaneously as a group from a preloaded needle. Third, it has been routine to employ a radiophysicist at the hospital to preload the implant needles and take a set of sample measurements of the strength of the radioisotope seeds to confirm that the seeds meet the requirements specified by the dose plan. Finally, due to the large number of low dose radioisotope seeds used in a given procedure (typically up to 150) and the need for the implanting physician to be able to modify the dose plan at the time of implant, it is generally considered that the flexibility afforded by manually loading the implant needles just prior to the operation provides the best possible treatment procedure for the patient and the most economically efficient procedure for the hospital.
Although manual preloading of implant needles at the hospital continues to be the norm for most low dose radioisotope procedures, relatively little attention has been paid to increasing the safety or efficiency of this process. Presently, the radioisotope seeds for a given dose plan are shipped in bulk in a protective container by overnight delivery to the hospital. At the hospital, the radioisotope seeds are dumped from the container onto a tray where the radiophysicist manually loads the seeds one-by-one into a set of implant needles according to the dose plan. Typically, the implant needles are positioned tip into a needle stand with the tips sealed with bone wax. The radiophysicist picks up a single radioisotope seed using a tweezers, forceps or vacuum hose and deposits that seed in a needle. Next, a single spacer made of gut or similar absorbable material is deposited in the needle. This process is repeated depending upon the predetermined number of seeds and spacers prescribed by the dose plan. The radiophysicist will use a well chamber to measure the strength of a sample of the radioisotope seeds (typically from only one seed to a sample of about 10%). While some needle stands are provided with a certain degree of shielding once the radioisotope seeds are loaded in the implant needles, there is very little shielding that protects the hands and fingers of the radiophysicist during the process of manually loading the implant needles.
Despite the various attempts to improve this process, the handling of radioisotope seeds for low dose radioisotope procedures remains a cumbersome process that can expose radiophysicists, physicians and other hospital personal to unshielded radioisotopes. It would be advantageous to provide for a radioisotope seed cartridge for transporting and handling low dose radioisotope seeds for use in low dose radioisotope procedures that could overcome these problems and enhance the safety and efficiency of this process.
The present invention is an automated cartridge for use in an automated system for low dose radioisotope procedures. The replaceable automated cartridge has a housing that contains a selectively positionable member having a plurality of radioisotope seeds preloaded in chambers defined in the positionable member. An aperture in the housing allows an elongated member to selectively eject radioisotope seeds from chambers in the positionable member when a given chamber is aligned with the aperture. A mechanism in the cartridge automatically positions the selectively positionable member in alignment with the aperture. Preferably, a feedback mechanism generates a positional feedback signal of a position of the chambers of the positionable member relative to the aperture.
In the preferred embodiment, a machine readable storage medium accessible via an electrical connector stores indicia representing at least the quantity and location of the plurality of radioisotope seeds preloaded into the cartridge. In this embodiment, each radioisotope seed is located in a unique chamber defined in the positionable member and each chamber is adapted to receive a seed, a spacer, a plug, or any combination thereof. The housing arrangement includes structure that mates with structure of the automated system. The positionable member is a rotatable drum having chambers defined around a periphery of the rotatable drum. A first stepper motor is operably connected to drive the rotatable drum, and a second stepper motor is operably connected to drive a linear actuator that operably drives the elongated member along a line of travel through a selectively indexed one of the chambers spaced around the periphery of the rotatable drum. An encoder is used to determine whether the stepper motor has rotated the rotatable drum to the correct chamber. Preferably, the stepper motor and encoder are selected such that the stepper motor steps in full steps with relation to the distance between chambers around the periphery. The alignment of the aperture to the chambers in the drum is preferably initially accomplished at the time of assembly.
In one embodiment, the automated cartridge is preloaded at a factory and shipped for usage with radioisotope seeds and spacers inside. In another embodiment, the automated cartridge includes a second aperture rearward of the selectively positionable member along the line of travel of the elongated member through which at least radioisotope seeds are introduced into the line of travel of the elongated member and loaded into the chambers in the selectively positionable member.